With regard to their main components, automated shift systems consist of conventional, sometimes even manually actuated shift systems in which the actuation of the shifting and/or starting clutch, between the drive engine and the transmission, and the selection and shifting of transmission gears is carried out automatically byway of corresponding actuating devices. These actuating devices are usually in the form of hydraulically or pneumatically actuated piston-cylinder arrangements or electric actuators, which act upon the control elements for the transmission functions.
In such piston-cylinder arrangements, a piston is fitted to move axially in a cylinder. The piston delimits a pressure chamber filled with a pressure medium and the piston can be in direct contact with the cylinder. Otherwise, sealing mechanisms can be arranged between the cylinder and the piston. When the piston-cylinder arrangement is actuated, the piston moves axially in the cylinder and as a result of adhesive sticking can be excited into uncomfortable and acoustically perceptible vibrations. To avoid such vibration, which is also referred to as the stick-slip effect, the surface of the piston is provided with a special lubricant. A disadvantage of this is that the stick-slip effect cannot be permanently eliminated by lubricating the surface of the piston and in particular not over the lifetime of a piston-Cylinder arrangement.
In the case of automated shift systems with a pneumatically or hydraulically actuated clutch or with foot-operated clutches with a pneumatic or hydraulic transfer path and pneumatic or hydraulic amplification, various influences can lead to stick-slip effects when the clutch is actuated including component wear, binding or contamination. Such influences can be present not just in the piston/cylinder arrangement, but also throughout the clutch actuation system. In addition, these influences can result in an increase of the hysteresis that exists when the clutch is released. The stick-slip effect can be manifested as a brief adhesion of the friction lining of a clutch disk to the opposed friction surfaces of the clutch pressure plates, followed by release of the static friction or when a piston-cylinder arrangement is actuated. It may result from adhesive binding between the cylinder and the piston. Static friction can also occur on contact surfaces in the mechanical transmission path where the direction changes or at bearing bolts. In the case of a gear change transmission designed as a claw transmission “tooth-over-tooth positioning” can take place. When clutch teeth are in a condition of mutual contact under stress and the vehicle's clutch is engaged so that the increasing torque turns the teeth relative to one another, the clutch teeth may mesh. Particularly in the case when a “tooth-over-tooth position” is resolved when at rest, when the clutch is brought from the disengaged condition to the locking position, increasing hysteresis can result in uncontrollable engagement movements of the clutch since the shifting force of the piston-cylinder arrangement must be reduced compared with the clutch force. If a clutch is in the locking position, then a small mount of torque is transmitted by the clutch.
DE 100 49 913 A1 discloses a transmitting cylinder for a hydraulic clutch or brake system. This transmitting cylinder consists of a housing in which a piston is arranged and can move axially. The piston delimits a pressure chamber filled with a hydraulic fluid and at least one sealing element is arranged between the housing and the piston. Preferably, the sealing element is positioned in a rotationally fixed manner on the housing of the transmitting cylinder. When the transmitting cylinder is actuated, the piston and the at least one sealing element are rotated relative to one another, preferably with the piston rotating relative to the sealing element. By way of this changed direction of movement when the piston is actuated, there occurs at the contact surface, between the sealing element and the surface of the piston, a modified transition from static to sliding friction, which largely avoids the stick-slip effect.
DE 100 49 913 A1 also discloses a second embodiment of the transmitting cylinder in which at least in a displacement zone of the at least one sealing element, the piston has a structured surface. In this way, the adhesive contact, between the sealing element and the piston surface can be minimized so that the excitation of vibrations, due to transitions from static to sliding friction, can also be minimized or eliminated.
For controlling hydraulic or pneumatic actuating means, pressure-generating and control devices are needed which, in accordance with the prior art, comprise a hydraulic or pneumatic pump as the pressure generating device, a pressure reservoir, a hydraulic or pneumatic control unit with control values and sensors, which are connected to a central control and regulation device and which can be actuated by the latter in accordance with control and regulation functions stored therein.
The disadvantages of the prior art are that with conventional piston-cylinder arrangements the stick-slip effect cannot be lastingly eliminated by lubricating the piston surface so that in the known solutions it is either necessary to superimpose rotational movement on the axial movement of the piston or to carry out costly machining of the piston surface to minimize or eliminate the excitation of vibration that results from the transitions from static to sliding friction. In addition, stick-slip effects that occur in a shift and/or starting clutch have an adverse action on the transfer behavior of the clutch.
The purpose of the present invention is to indicate a method for the control of an actuating device by which the disadvantages of the prior art are minimized or eliminated.